Removal and recovery of solvent



April 23, 1940. D. McDONALD REMOVAL AND RECOVERY OF SOLVENT Filed Jan. 2,1935 2 Sheets-Sheet 1 A ril 23, 1940,

D. M DONALD REMOVAL AND RECOVERY OF SOLVENT Fiied Jan. 2. 1935 2' Shets-Sheet 2 INVENTOR.

Patented Apr. 23, 1940 UNITED STATES PATENT OFFICE 2,198,412 REMOVAL AND Recover? or SOLVENT Dan McDonald, Los Angeles, Calif., assignor, by mesne, assignments, to Engineering Incorpo;

rated, a corporation of California Application January 2, 1935, Serial No. 59

14 Claims.

my copending application Ser; No. 639,200, filed October 24, 1932, and also includes certain features of invention which are not disclosed in said copending application.

' The solvent, such as carbon tetrachloride or trichlorethylene, is evaporated from the materi- 15 als after having removed oils; greases, etc., and

may then be recovered for reuse, the solvent and its vapors being preferably circulated under partial vacuum in aclosed system so as to simplify the apparatus and avoid loss of solvent vapors.

The solvent which has dissolved'oils, grease and the like, and which has then been removed from the materials being cleaned, may be regenerated by distillation, and heat from the vapors of distillation may be utilized as the latent heat which 5 is absorbed by the solvent vapors when evaporating from the materials. As a consequence the solvent which is to be evaporated from the materials may be maintained at boiling temperature to insure rapid evaporation and thorough drying of the materials, and the evaporating SO11 vent having absorbed a part of the heat of the vapors of distillation, these distilled vapors may be subsequently condensed and returned to storage with economical operation of the condenser. The heat energy generated in the still may be utilized for superheating the distilled vapors which supply the latent heat for evaporating the solvent from the materials, so that the distilled vapors are at such temperature as will supply the necessary heat for evaporating the solvent and still leave the distilled vapors at a temperature which will avoid their condensation while supplying the necessary heat of evaporation.

The same result may be accomplished, i. e.,

the vapors from the still may be supplied to the steam for example, for supplying latent heat oi. evaporation, with the partial vacuum in the system lowering the boiling point of the solvent so that the vapor may be economically supplied at such higher temperature as will evaporate the 5 solvent. When steam is employed, it displaces all traces of the solvent so as to'freshen and deodorize the materials.

centrifuging may also be employed for ex-' tracting solvent from the materials, with vapors 10 vaporized liquid to said closed space, with lower 20 pressure maintained at the exterior of the annular layer of materials, whereby the pressure differential insures the vapors, steam for example, passing through the compact materials in'intimate contact with all portions thereof, 25 with a relatively small volume of steam evaporating all traces of the solvent which still impregnates the materials.

It is a still further object of the invention to operate the system under partial vacuum so that 80 the solvent vapors are drawn from the still and from the materials which have been cleaned, into a. condenser, and thence to the means which is employed for creating the partial vacuum; in order that the vacuum creating means need not 35 have the large capacity which would be required if solvent vapors were first handled by the vacuum creating meansand subsequently condehsed.

A balanced system may thus be employed, with the solvent which is withdrawn from the materials and which is then regenerated bydistillation, supplying suflicient heat to vaporize all the solventremaining in the materials, and with all or the solvent vapors then condensed and returned to storage for reuse in the cycle of operation, the entire cycle of operation being maintained by a vacuum creating means of relatively small capacity, since the vacuum creating means fore they have been condensed.

Further objects of the invention will be readily understood from the following description of the accompanying drawings, illustrating the invenl5 is not required to handle the solvent vapors betion in somewhat diagrammatic form and in which:

Fig. 1 illustrates one embodiment of apparatus for carrying out the invention,

Fig. 2 illustrates a modified embodiment of such apparatus.

A solvent, such as trichlorethylene, adapted to remove grease, oils, etc., from fabrics, meal or other material, is supplied to a container for the material, the container being shown as a horizontal cylinder I such as employed for dry cleaning garments and extracting oil from meal. The cylinder is preferably jacketed as shown at 2, and has an inner revolving cage 8 in which the material to be treated is placed for tumbling action when the cage is revolved. The solvent is supplied to cylinder I through a pip 4 having a valvular control 5, and the cage 81s perforated or of screen construction so that the materials are agitated and immersed in the solvent whenthe cage is revolved. After the solvent has removed oil, grease, etc., the materials are dried and deodorized in the container.

As illustrated at Fig. 1 a drain pipe 6 for the liquid solvent leads from the bottom of cylinder I and is provided with a valvular control I, and a pipe 8 for solvent vapors leads from the top of cylinder I and is provided with a valvular control 8. The liquid solvent which is drained oil through pipe 6 is regenerated by distillation, with the distilled vapors then condensed and returned to storage for reuse; and the solvent. vapors 4 which are withdrawn through pipe 8 are also condensed, preferably in the same condenser, and are then preferably returned to the same storage receptacle for reuse. As an instance of this arrangement a still I 0 may be positioned alongside the container I, with a storage tank II above the container and a condenser I2 above the storage tank. The drain pipe 6 leads to the still, preferably through a lint trap I I, and a pipe I4 for distilled vapors leads from the still to the condenser I2 and is provided with a valvular control It. The pipe 8 also leads to the condenser, preferably through a lint trap 80. and the condensed solvent is. withdrawn from the condenser to the storage tank II by a pipe I8.

The system as thus described ts a closed system, and for economy and rapidity of evaporation, distillation and subsequent condensation, a partial vacuum is maintained in the system during the drying operation, and this partial vacuum is adapted to circulate the solvent through the system. As an instance of this arrangement storage tank II is connected to the intake of a vacuum pump II by a pipe I8 having a valvular control I9, so that'the vacuum pump is adapted to create a partial vacuum in the closed system. The solvent is withdrawn as vapor through pipe 8 and thence through the condenser to the storage tank; and is withdrawn in liquid phase through pipe 6 and is then vaporized in still ID from whence the distilled vapors are drawn through pipe I4 to the condenser and the storage tank. A sight glass 20 may be provided on the storage tank for observing flow of solvent and noting the level of 'any water accumulating in the storage tank above the solvent; and the sight glass is preferably provided with drain cocks 2| so that by opening a cock above the solvent level and at the same time opening a vent 22 on the storage tank, the accumulated water may be periodically drained off. The supply pipe 4 leads from the bottom of the storage tank and is adapted for gravity flow of solvent to the cylinder I; and in order to avoid a vortex being formed at the mouth of the supply pipe while the solvent is being withdrawn, such as might result in water being drawn from above the solvent into the supply Pipe. the mouth of the pipe is preferably an enlarged bowl 23 adapted to draw off thesolvent from the storage tank with no appreciable agitation. A valve 83 which cooperates with a valve seat 82 may control withdrawal through pipe 4, and the valve is float actuated as shown at ,with the float adapted to sink in water accumulating in the storage tank above the solvent level but adapted to float on the surface of the solvent, so that the valve is normally open but will close in the event of the solvent level a being so lowered as to result in water instead of solvent being withdrawn at the pipe I.

The vacuum pump I1 is illustrated as of the type shown in my U. 8. Letters Patent No. 2,022,682,'-granted December 3; 1935. As an instance of this construction the pump casing may contain a quantity of the same-kind of solvent as has been used for dissolving oil and grease from the material contained in the cage 8, e. g., trichlorethylene, and this body of fluid, shown at 28, is drawn into the rotor 25 of the pump and is discharged from the periphery of the rotor so as to create a partial vacuum at the pump intake 26 which communicates with the pipe I8. Fluid is thus drawn into the pump through the pipe I8 and is discharged from the periphery of the rotor. The solvent andany water in the system, having passed through the condenser I2, will substantially all be in liquid phase when collected in the storage tank II, and the fluid withdrawn via the pipe I8 which communicates with the upper portion of the storage tank above the outlets for the liquid solvent and the water, will'thus comprise the air in the system which it is desired to exhaust in order to create a partial vacuum, free of solvent and water except for any slight traces of solvent which have not condensed and collected in the storage tank but which are drawn through the pipe I8 while still in vapor phase. The air, with any slight traces of solvent vapors, which is thus drawn into the pump and discharged from the periphery of the rotor 25, is compressed in the closed pump casing so as to condense any traces of solvent vapors. Excess of solvent accumulating in the pump casing may be drained ofl! and returned to storage tank II via a pipe 32 having a float-controlled valve 33.

In order to prevent loss of any slight trace of solvent vapors which may escape at the outlet 29, a trap 34 is preferably connected to the outlet, and may be filled with water and have baflles 34', with the outlet 29 connected to the lower end of the trap by an inverted U-pipe 85. The water in the trap th'us condenses any last traces of solvent, with the solvent condensate settling below the water so that the water seals against escape of solvent vapors, while permitting air to bubble upwardly through the water seal and finally discharge to the atmosphere via a vent 84'. Any solvent vapors which are thus condensed in the trap, may be returned to storage tank II via a pipe 38 leading from the bottom of the trap and having a valvular control 31.

The solvent vapors from still ID are adapted for return to cylinder I, as well as being adapted for flow through the pipe I4 to the condenser I2; and for this purpose a pipe II leads from the still to the cylinder I, and is provided with a valvular control 42. The vapors in pipe 4| may be superheated by means of a heat exchanger as which the vapors are adapted for return to cylinder I extends through the heat exchanger 41 so that the temperature of the vapors is appreciably increased by the higher temperature to which the water circulating through the heat exchanger has been raised by the burner 44.

Means are also provided for injecting steam into cylinder I; and for this purpose a pipe 50 projects into the lower portion of thecylinder and is providedwith jet openings'SI, and steam is supplied to pipe 50 through a steam line 52 having a valvular control 53. The jacket 20f cylinder I is a heating jacket, and steam may be applied thereto from'the steam line 52,-as for. example through a branch line 54 having a low pressure regulator 55 and a valvular control 56.

When operating the plant, materials such as garments to be dry cleaned, or rags, waste, etc., from which grease and oil are to be removed, or meal from which oil is to be recovered, are placed in cage 3, the outer cylinder I is then closed, and solvent such as trichlorethylene is supplied to cylinder I from storage tank II by opening the valve 5 in the supply pipe 4. The valve 5 is then closed and the cage 3 is revolved, the valves I and 9 being closed so that the solvent is confined in the container, and the valves 53 and 56 being also closed. The valve 42 is closed so that the Y still I0 is not in communication with the container; and if all the solvent from a previous operation has been regenerated, the valve I5 is also closed so that the still I0 is idle, but the pump I1 is preferably in operation with the valve I9 open, so as to maintain a partial vacuum in that part of the system which includes the condenser I2 and the storage tank I I.

When the solvent has removed the grease, oil, etc., from the materials in the container, it is drained off and regenerated in the still I0, and the remaining solvent is evaporated'so as to completely dry and deodorize the materials, with the cage 3 preferably continuing to revolve during the drying operation.

At the start of the drying operation valves 1 and I 5 are opened and steam is supplied to jacket '2 by opening valve 56. thereby heating and expanding the solvent in cylinder I. I thus created in the cylinder, so that the partial vacuum in the circulating system drains off liquid solvent through the pipe 6. and the solvent is vaporized in the still III which has been put into operation, and the solvent vapors may then be drawn into condenser I2 through the pipe I4, from whence the condensate is returned to storage tank II. I

When all of the liquid solvent has been drained ofi, thevalve I is closed and valve 9 is opened so that the partial vacuum in the circulating system evaporates solvent from the container I and withdraws the solvent vapors through pipe 8 into condenser I2, from whence the condensate is returned to storage tank I I. At the same time distillation of the liquid solvent which has been drawn into still III is continued, and these solvent Pressure is p vapors may be returned to the condenser via pipe In lieu of return of solvent vapors from the still I0 to the'condenser I2 via the pipe I4 thus far described, all, or at least a part of the solvent vapors from the still, may be returned to the container I and thence to the condenser I2, so that the heat of the regenerated solvent which would otherwise be a waste product which would have to be handled by the condenser I2, is utilized for supplying latent heat forvaporizing remaining liquid solvent in the container. I. For this purpose the valve I5 is closed and the valve 42 is opened at such time during the cycle of operation that the vapors of the distillation process which are then returned to the container I before passage to the condenser I2, will be sufiicient to vaporize all remaining liquid solvent in the container I, thus providing a balanced system. The

heat of the regenerated solvent which is thus utilized, may be increased by superhe'ating the solvent vapors coming from the still. For this purpose the vapors from the still I0 may pass through heat exchanger 41 and are then returned to cylinder, I via pipe 4I. These superheated solvent vapors thus furnish the heat of vaporization absorbed by the solvent when evaporating, and thus maintain the solvent at boiling temperature so that evaporation is not retarded. By superheating the distilled vapors in the heat exchanger, they are readily and economically raised to a temperature adapted to supply the heat of vaporization absorbed by the evaporating solvent, and still leave the distilled vapors at a temperature above their dew point so as to avoid condensation in cylinder I.

After the valve 42 has been opened and evaporation of solvent has been continued until substantially all of the solvent has been extracted, the valve 42 is closed and the valve 53 in steam line 52 is opened. The line 52 carries dry steam.

under appreciable pressure which is discharged all traces of the solvent being vaporized and withdrawn.

The steam may be injected for approximately two minutes so as to leave the garments fresh and dry and with no odor of solvent, and all of the solvent vapors having been drawn off through pipe 8 and returned to storage tank II, valves 9 and 53 are closed, and after a vent SI on cylinder I has been opened the garments are removed.

While the preferred operation is that as described, with the steam lntroduced subsequent to introduction of superheated solvent vapors of the distillation process, it will be understood that with certain materials steam may be used alone and in lieu of superheated solvent vapors for supplying latent heat for evaporating solvent from the materials, and that while solvent vapors of the distillation process and steam have been particularly described for supplying this latent heat, any suitable liquid having a boiling point at leastas high as that of the solvent, might be vaporized in a suitable apparatus (not shown), and supplied to cylinder I at a temperature higher than that of the solvent therein, for evaporating the latter.

In the modification of the invention shown'at Fig. 2,'drain pipe I06 leads from cylinder I to a trap I I 3 and is provided with a valvular control valvular control I 5. Condensate is returned from the separator to the still through a pipe I22. The pipe 8 also leads to the condenser I 2', and from the condenser solvent is discharged into a storage tank I I through a pipe I0".

and collects any water accumulating in the solvent storage tank, the water tank being provided with a drain I82. A supply pipe 4* leads from the tank II to the cylinder I and is provided with a valvular control 5.

The storage tank I I e is connected by pipe I3 to the intake 26 of a vacuum pump I'I such as previously described, the pipe I8 having a valvular control I9. Solvent condensate from the pump casing may be returned to storage tank II via a pipe 32 A pipe I80 connects the cylinder I and the pipe I8 and has a valvular control I0l; and the cylinder I has a vent 6|.

Solvent vapors fromv still I0 may be returned to cylinder I through a pipe li leading from the separator I and having a valvular control 42'; and the vacuum pump I'I draws fluid through the system either from cylinder I via pipes I06 and Ii, still I0, and pipes I4 and I2] to the condenser II", or from still I09, via pipes I4 and 4|, cylinder I, and pipes I06 and 8 to the condenser I2 depending upon selective manipulation of the valvular controls as hereinafter described. From the condenser pump draws fluid through the pipe I6- into the storage tank II with the pump I'I maintaining a partial vacuum via the pipe I8, and with substantially all of the solvent and any water in the system collecting in the storage tank II in liquid phase, having passed through the condenser, and with the pipe I8 which communicates with the upper portion of the storage tank above the outlets for the liquid solvent and the water, thus drawing oif the air in the system which it is desired to exhaust in order to create a partial vacuum in the system, with the air free of solvent and water, except for any slight traces of solvent which have not condensed and collected in the storage tank but which are drawn through the pipe. I8 while still in vapor phase. The still I0 is at a point in the system further away from the vacuum pump than the cylinder I when the flow is from the still I 0 via pipe II, cylinder I, pipe 8" and thence to the condenser, so that a higher vacuum is maintained in cylinder I than in the pipe The pipe ll may discharge into cylinder I through a hollow rotatable shaft I50 on which cage 3 is mounted, the hollow shaft being provided with jet openings 5|. Steam may also be discharged into cylinder I through the jets SI", as for example via a steam line 50 which has a valvular control 53*. The steam may be supplied from a line 52, which may also supply steam to jacket 2, through a branch line 84'- having a low pressure regulator 55 and a valvular control 56'.

The cage 3 may be revolved at slow speed by a motor Ill during the time that the materials in the cage are being treated with solvent; and dur ing subsequent evaporation of the solvent the A tank I60 communicates with tank I I i as shown at ISI,

I 2- the vacuum.

cage 3 may be revolved at high speed by a motor I'll in order to extract solvent by centrifuging.

In operation, with the vent 3i and the valves Ill, 3'', l2- and Ill closedrthe cage 3 is charged with the material which is to be treated with a suitable solvent, and the cylinder I is then closed.

Solvent is supplied toicylinder I from storage tank II' by openlng valves 5 the valve III being also opened to permit gravity how of the solvent. The valves 3* and III are then closed and the cage 3 is slowly revolved by the motor IIl until the solvent has dissolved the oil. grease or the like which it is desired to remove from the material in the revolving cage. The valves Ill and 1" are then opened and with valves 42* and 0' closed, solvent is drainedfrom cylinder I via pipe I 03 and is drawn into the still I0 via pipe 3, by the vacuum created in the system by opening the valves' I 5" and I0 and operating the vacuum pump Il When solvent no longer shows at a sight glass I 90 in the pipei, the cage 3 is'revolved at high speed by means of the motor I" in order to extract additional solvent by centrifuging; and when sight glass I shows that no further solvent is being extracted the valve 1 is closed. If a rinse is desired the valve 5' is opened and the operation as thus far described is repeated; and when solvent no longer shows at sight glass I80 the valve 1 is again closed. The solvent drawn into still I0 is vaporized, with the vapors of distillation flowing through pipes I4 and I2I into condenser I2, and the condenser solvent returning thence to storage tank II.

Any solvent remaining with the materials incage 3 is now removed by evaporation. with the motor I10 preferably rotating the cage at high speed during this evaporation, and with steam supplied to the jacket 2 via the valve 66. Valves 3' and 42* are opened and the valve I5 is closed, valve I0I remaining open and valve I remaining closed so that vapors from the still do not flow to the condenser I! but are returned to cylinder I via pipe I and the flow is thus from the still III to the cylinder I and thence via pipe 0* to the condenser I2. As previously described, when the flow is via this route, the vacuum pump I'I' maintains a higher vacuum in cylinder I than in pipe ll, andtherefore the dew point of the vapors in the cylinder, which are heated to the boiling point by the steam in jacket 2. is lower than that of the vapors o1 distillation in the still I0 and the pipe II. The vapors returned via pipe ll therefore have a higher temperature than the boiling point of the solvent in the cylinder, and these vapors are dry enough and the pressure diflerential is such that the higher temperature of the vapors will furnish the heat of vaporization absorbed by the solvent when evaporating, while still leaving the distilled vapors at a temperature above their dew point so as to avoid condensation in cylinder I.

After or in lieu of returning the vapors of distillation to cylinder I to supply heat oi vaporization, steam may be supplied to cylinder I, the valve 42! being closed and the valve I5 opened, with the valves I01 and 0' remaining open and the valve 1' remaining closed, so that vapors from the still I 0 flow to the condenser I2, and the valve 53* being opened to discharge steam from the jets ii into the cage 3. Since the sol vent in cylinder I is under appreciable vacuum. its boiling point is lowered so that the temperature of the steam which is introduced is considerably above the boiling point of the solvent.

A small portion of the steam is condensed, displacing the solvent from the materials in cage 3, and the steam supplies latent heat of vaporization to evporate any remaining solvent and thoroughly dry the materials.

By rapidly rotating the cage 3 while solvent is being evaporated, the materials in the cage are -;condensate so that the partial vacuum increases in the direction offlow of the solvent vapors held against the perforated peripheral wall of the I cage, and the ends of the cage being imperforate the materials form an enclosure into which jet orifices 5| discharge. The vapors of distillation and/or the steam discharged at the jet orifices must therefore pass through the materials at the I periphery of the revolving cage before they discharge via pipe I06 for return to condenser l2,

so that solvent is extracted by centrifuging and at the same time is rapidly displaced and evaporated by the vapors of distillation and/or the steam.

In this form of the invention and in connection with certain materials it is also possible to utilize vapors other than steam or solvent vapors of the distillation process for supplying latent heat, any suitable liquid having a'boiling point at least as high as that of the solvent being vaporized insuitable apparatus (not shown), with said vapors supplied to the cylinder l at a temperature higher than that of the solvent in the cylinder, for evaporating the solvent. I claim:

1. In combination, a container for material from which soluble substances are to be removed by use of a liquid solvent, a storage tank for the =liquid solvent, a supply pipe leading from the storage tank to the container, a still for regenertrols for closing the drain pipe and adapting the vacuum pump to maintain a partial vacuum in the system, increasing along the solvent vapor supply pipe from the still toward the container and thence successively toward the condenser, storage tank and vacuum pump, whereby solvent vapors of the regeneration process are supplied from the still to the container at a higher temperature than the boiling point of the liquid solvent in the container for vaporizing said solvent, with the vaporized solvent then withdrawn from the container and condensed andreturned to storage.

2. In a method of removing and recovering solvent from material from which soluble substances have been displaced'in a system utilizing distillation for regeneration of the solvent used; the steps including: centrifuging the material while confining the same so as to define a closed annulus, conducting'solvent vapors of the distillation process to the interior of the closed annulus,-

withdrawing solvent vapors from the material through the closed annulus of said material, condensing said solvent vapors, and maintaining the system under partial vacuum exerted on'the I and whereby the solvent vapors of the distillation process are conducted to the interior of the closed annulus of material at a higher temperature than the boiling point of the solvent in said material for vaporizing said solvent.

3. Ina method of removing and recovering solvent from material from which soluble substanceshave been displaced by use of a solvent; the steps including: centrifuging the material while confining the same so as to define a closed annulus, vaporizing a liquid which has a boiling point at least as high as that of the solvent, conducting vapors of said vaporization process to the interior of the closed annulus of material, withdrawing solvent vapors from the material through the closed annulus of said material, condensing said solvent vapors and maintaining the system under partial vacuumexerted on the condensate so that the partial vacuum increases inthe direction of flow of the vapors and whereby the vapors of the vaporization process are conducted to the interior of the closed annulus of material at a higher temperature than the boiling point of the solvent in said material for vaporizing said solvent.

4. In a method of drying material from which soluble substances have been displaced by use of a solvent; the steps including: centrifuging the material while confining the same so as to define a closed annulus, and discharging steam into the interior of the closed-annulus of material while maintaining a partial vacuum at the exterior of the closed annulus of material, whereby the solvent in the material is vaporized and withdrawn through the closed annulus of material.

5. In a method of drying material from which soluble substances have been displaced by use of I a solvent; the steps including: centrifuging the material while confining the same so as to define a closed annulus, and supplying vapor of a liquid,

which has a boiling point at least as high as that of the solvent, tothe interior of the closed annulus of material while maintaining a partial vacuum at the exterior of the closed annulus of material, whereby the solvent in the material is vaporized and withdrawn through the closed annulus of material.

6. In combination, a container, a cage in .the container for material treated with a 1iquid,solvent, the cage having a perforated periphery and closed ends, meansfor rotating the cage to main- .taina closed annulus of the material against the perforated periphery of the cage, with the ends of said annulus closed by the ends of the cage, 8. still for regenerating the solvent used,

means for conducting liquid solvent from the container to the still, means for supplying solvent vapor from the still to the-interior of said closed annulus, a condenser having an inlet and an outlet, the inlet of the condenser being con-. nectedto'the container, and means for maintaining a partial vacuum in: the system increasing from the still toward the interior of said closed annulus and thence through the material and into the container and thence toward and through the condenser and thence towardthe vacuum maintaining means.

7. In combination, a container, a cage in the container for material treated-with a liquid solvent, the cage having a'perforated periphery and closed ends, means for rotating the cage to main.-

of said annulus closed by the ends of the cage, a condenser having an inlet and an outlet, the inlet of the condenser being connected to the contain a closed annulusof the material against the perforated periphery of the cage, with the ends tainer, means communicating with the outlet of the condenser for collecting condensate, means for maintaining a partial vacuum in the system increasing through the closed annulus oi! material into the container and thence toward and through the condenser and thence toward the condensate collecting means, the partial vacuum being exerted above the condensate in said collecting means, and means for supplying steam to the interior oi! said closed annulus of material for contact with said material.

8. In a method of removing and recovering solvent from material from which soluble substances have been displaced in a closed system utilizing distillation for regeneration of the solvent used; the steps including: agitating the material, providing decreasing pressure in one direction through the closed system for preventing opposite flow of gas or vapor, conducting solvent vapor of the distillation process to the material in the direction of decreasing pressure for-contact with the agitated material at higher temperature than the boiling point 01' the solvent in the material while continuing to agitate the material, withdrawing all gas and vapor from the material in the direction of decreasing pressure, condensing the withdrawn vapor, and withdrawing all condensate and non-condensables in the direction of decreasing pressure.

,9. In a method of drying material dampened with a solvent for oil and the like, the steps including: centrifuging the material while confining the same so that it extends around an interior space defined by said material, in such manner that a fiuid'can escape from the space only through the material and supplying a vaporized liquid to the interior space while maintaining lower pressure at the exterior of the material for flow of vapor from the interior space through the material and to the zone of lower pressure for vaporizing solvent in the material.

10. In a method of drying material dampened with a solvent for oil and the like, the steps including: centrifuging the material while confining thesame so that it extends around an interior space defined by said material and also defines a space extending around said material at the exterior thereof, in such manner that a fluid can pass from one such space to the other only through the material and supplying a vaporized liquid to one of said spaces while maintaining lower pressure in the other of said spaces for flow of vapor from said one of said spaces through the material and to the zone of lower pressure in said other of said spaces for vaporizing solvent in the material.

11. In a method of drying material dampened with a solvent for oil and the like, the steps including: oonfinins the material so that it extends around an interior space defined by said material and also defines a space extending around said material at the exterior thereof, in such manner that a fluid can pass from one such space to the other only through the material and supplying a vaporized liquid to one of said spaces while maintaining lower pressure in the other of said spaces for flow oi vapor from said one of including: centrifuging the material while confining the same so that it extends around an.

interior space defined by said material and also defines a space extending around said material at the exterior thereof, and supplying vapor of a liquid which has a boiling point at least as high as that of the solvent, to one of said spaces while maintaining a partial vacuum in the other of said spaces for flow of vapor from one of said spaces through the material and to the zone of partial vacuum in said other of said spaces for vaporizing solvent in the material.

13. In a method of drying material dampened with a solvent for oil and the like, the steps including: centrifuging the material while con fining the same so as to define a complete annulus with closed ends, supplying a vapor of a liquid, which has a boiling point at least as high as that of the solvent, to the interior of the closed annulus of material while maintaining lower pressure at the exterior of the closed annulus of material, whereby solvent in the material is vaporized and withdrawn through the closed annulus of material to the zone oi lower pressure at the exterior thereof.

14. In a method of removing solvent from pieces of material, 'the steps of: forming a body from a plurality of pieces of material dampened with a solvent upon a movable perforated support within an enclosed zone and in the virtual absence of a body of liquid solvent in such manner that the zone is divided by the body and support and the divided parts of the zone communicate only through the body and support; supplying heat to said zone; and supplying hot drying vapors of a liquid which has a boiling point at least as high as that of the solvent to said enclosed zone on one side of, said support while maintaining a lower pressure on the other side of-said support to establish flow of said drying vapors through said body of pieces of material for vaporizing solvent in said material.

DAN McDONALD. 

